Petrography and Geochemical Characteristics of Carbonatites and Associated Rocks in Southern Part Obu Opkela, Edo State

Abstract

Carbonatites are rare igneous rocks of mantle origin that are characteristically enriched in CaO and incompatible elements such as rare earth elements , Sr, Ba, and Nb, and they represent important hosts for strategic and industrial minerals. Field mapping reveals that the carbonatites occur as discrete intrusive bodies emplaced within granitic and migmatitic basement rocks, with associated pegmatite veins. Petrographic analysis indicates that the carbonatites are dominantly calcitic, characterized by coarse-grained calcite with accessory apatite, pyrochlore, biotite, and minor sulphides, while textural evidence of secondary dolomitization reflects late-stage hydrothermal modification. The granitic host rocks display typical quartz–feldspar assemblages with evidence of deformation and alteration along structural zones. Geochemical data obtained from X-ray fluorescence analysis show very high CaO contents (up to ~95 wt.%), low SiO2, and variable but generally low MgO, confirming the carbonatitic nature of the rocks. Trace element patterns reveal enrichment in REE, Sr, and Nb, with REE distributions largely controlled by apatite-rich zones, while Nb enrichment is localized and associated with pyrochlore-bearing domains. Primitive mantle- normalized spider diagrams display enrichment of large-ion lithophile elements and depletion of high-field-strength elements such as Zr, Hf, and Ti, consistent with continental carbonatite systems affected by crustal interaction. The absence or low detection of MgO and heavy rare earth elements in some samples is interpreted as reflecting primary calcitic carbonatite compositions and mineral-controlled elemental partitioning rather than analytical or sampling bias.

References